The invention relates to a printed circuit board (PCB) for surface mounting of electrical and/or electronic components, in particular an SMD (surface mounted device) antenna with a ceramic substrate and at least one resonant conductor track structure. The invention also relates to such an antenna for single and multiband applications, in particular in the high-frequency and microwave ranges.
Electromagnetic waves in the high-frequency and microwave range are used for transmitting information in mobile communications. Examples of this are the mobile phone bands which lie in the range between approx. 880 and 960 MHz (GSM 900) and between approximately 1710 and 1880 MHz (DCS 1800) and around 1850 and 1990 MHz (PCS 1900) in Europe, the GPS navigation signals which are emitted in a frequency band at approximately 1573 MHz, and the Bluetooth band in the frequency range between approximately 2400 MHz and 2500 MHz which is used for data exchange between individual terminals. Thus firstly a strong trend can be detected towards miniaturization of communication devices and their components and secondly the aim is to equip these devices with more and more functions (multifunctional devices). This concerns, for example, mobile phones which are combined with a receiver module for GPS navigation signals and a Bluetooth module for data communication with other terminals.
The generally accepted surface mounting (SMD method) of the electronic components on the printed circuit board (PCB) and the increasing integration of individual modules do indeed achieve a good degree of miniaturization. An essential problem in relation to further miniaturization is, however, the space required for the components and in particular the antennae, as the latter must have a particular minimum size in order to form an electromagnetic resonance, in general a length of at least one quarter of the wavelength of the radiation emitted. This problem can be partially solved by the use of a dielectric carrier material (substrate) with as high a dielectric constant ∈ as possible, because then the wavelength in the substrate is reduced by a factor 1/{square root over (∈)} and a corresponding reduction in dimensions of antenna by this factor is possible.
EP 0 790 662 discloses, for example, an antenna structured in view of the above with a substrate and an L- or U-shaped radiant electrode and a power supply electrode. The radiant electrode is short-circuited with one end to a ground potential and is spaced by a gap from the power supply electrode at this end. The free end of the radiant electrode here has a distance from the supply electrode such that the two are electrically coupled by a capacitance formed by the gap. Due to the shape of radiant electrode and the manner of coupling, an antenna can be achieved with particularly small dimensions.
A further problem in connection with said integral applications arises in that multiband antennae are required for this which can be operated in each of the frequency bands used and must have a corresponding bandwidth. As the bandwidth of an antenna decreases as the dielectric constant of the substrate material rises, however, there is a particular minimum antenna size and hence a particular minimum size of circuit board on which the antenna is mounted if a required bandwidth is to be retained.
A general object of the invention is to find a possibility of further reducing the size of a printed circuit board which carries the essential electrical and/or electronic components for a communication device of the type mentioned above.
In particular, the invention is to provide a single or multiband antenna which allows further miniaturization of the printed circuit boards. Furthermore, a single or multiband antenna is to be created which in particular has an adequate bandwidth for use in one or more of the above frequency bands without requiring substantially greater dimensions.
Finally, a multiband antenna is to be created which is relatively easy to define as regards its resonant frequency.
The object is achieved as claimed in claim 1 with a printed circuit board for surface mounting of electrical and/or electronic components, in particular an SMD antenna with a ceramic substrate and at least one resonant conductor track structure, which is characterized in that the printed circuit board has a ground metallization substantially surrounding the antenna, and one end of the conductor track structure of the antenna is connected to the ground metallization.
A first advantage of this solution is that the ground metallization surrounding the antenna allows the other components of the circuit board to be arranged closer to the antenna, and hence the dimensions of the board can be reduced with the same number of components. The adaptation problems normally occurring due to ground metallization are largely avoided in that the track structure is connected not to a supply for electromagnetic waves to be emitted, but to the ground metallization.
This connection at the same time has the further advantage that an antenna with an essentially greater bandwidth can be achieved thereby without a substrate with a lower dielectric constant having to be used. The dimensions of the antenna consequently need not be enlarged in comparison with a relatively narrow-band antenna or are smaller than in a conventional antenna with the same bandwidth.
The object is also achieved in accordance with claim 1 with an SMD antenna with a ceramic substrate with at least one resonant conductor track structure which is characterized by a first supply lead for connecting one end of a first resonant track structure of the antenna to a ground potential and a second supply lead for coupling an electromagnetic wave to be emitted into the antenna, wherein the first conductor track structure has a plurality of conductor sections and where the length of the conductor track structure is suitable for exciting a desired first resonant frequency (base mode), and the course and distance of the conductor sections is chosen such that a first harmonic of the base mode can be excited.
In addition to the above advantages, this solution has the further advantage that a dual band antenna can be implemented in this relatively simple manner.
The dependent claims relate to further advantageous embodiments of the invention.
With the design as claimed in claim 1, a three-band antenna can be produced which is suitable in particular in the integrated communication devices of the type mentioned in the opening paragraphs.
The design as claimed in claim 2 has the advantage that the excited antenna resonances are particularly pronounced, while with the design as claimed in claims 3-7 in particular an electrical adaptation of the antenna can be optimized.